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2 I 6                    THE AFFINITIES OF TOXOBONS                    CHAP.

There is no doubt about the close alliance of the two genera
just referred to. It is more doubtful whether Homalodonto-
therium and its allies should be placed, as they often are, in the
neighbourhood of the Toxodonts. Hbmalodontotheriuni owes its
name to its even row of teeth without a diastema. It was a
creature of equally large size with Toxodon, and also came from
the Tertiary strata of Patagonia. The teeth are the typical forty-
four, and the molars like those of a Rhinoceros; they are, how-
ever, brachyodont and not hypselodont as in Toxodon. This genus,
however, shows an important difference from the Bhinocerotidae
and from the other Toxodontia in the fact that it was five-toed, and
that the bones of the carpus and tarsus are set in relation to each
other in the linear serial fashion.

Undoubtedly a near relative of Sowialodontotlierium is dLstrapo-
fheriutn,. This creature was of equal bulk, and was also Patagonian
in range. The teeth are reduced in number, "but the animal was
provided, like a Wild Boar, with great tusks, which were, however,
formed by the Incisors. This animal is very imperfectly known;
it is the form of the molars and the large size of the incisors which
have led to its association with the Toxodontia. As to the resem-
blance of the teeth of this genus and of HomcLlodontotJi&yiu'm to
those of Jfthinoceros, it is difficult to regard it as evidence of near
affinity. The likeness is probably to be looked upon as a case of
parallelism in development. Exactly the same explanation is
possibly to be given to the likeness which the teeth of Toxodon
and Wesodon show to Hodents, or even to Edentates. As to their
affinities Zittel observes :

*'The entirety of their osteological characters argues for the
Toxodon a separate position in the neighbourhood of the Perisso-
dactyla, Proboscidea, Typotheria, and Hyracoidea. The relations
to the Rodentia rest mainly upon the converging development of
the teeth, not upon tntie relationship."

Ijarge vegetable-feeding animals, usually scantily covered with
hair, and with the nostrils and upper lip drawn out into a long
proboscis. Digits five on both limbs. Femur and humerus not
bent upon lower leg and fore-arm in a position of rest. Skull